Gas wiping nozzle for a wire coating apparatus

ABSTRACT

A gas wiping nozzle for a wire coating apparatus includes an inlet portion defining a converging inlet passage for a coated wire that is axially drawn through the gas wiping nozzle. A wiping portion is further included and defines a wiping passage for the coated wire, downstream and in an axial extension of the inlet passage. The wiping portion has a gas outlet surrounding the wiping passage for blowing wiping gas onto the coated wire. A protruding annular lip is arranged between the converging inlet passage and the wiping passage, and the annular lip defining a passage for the coated wire that is narrower than the wiping passage so that the gas outlet means in the wiping passage is protected by the protruding annular lip against direct contact with the coated wire which is axially drawn through the passages of the wiping gas.

FILED OF THE INVENTION

The present invention relates to a gas wiping nozzle for a wire coatingapparatus.

BACKGROUND OF THE INVENTION

A metallic wire is commonly coated by passing the wire through a bath ofmolten metal, such as molten zinc, molten zinc alloy, or moltenaluminum. After emerging from the molten metal bath, the wire is drawnthrough a gas wiping nozzle, in order to obtain a uniform metal coatingupon the substrate metal, by wiping the excess of molten metal.

Such a gas wiping nozzle is e.g. disclosed in EP-A-0 357 297. The nozzlehas an upper annular part and a lower annular part. Each of the annularparts have an upper and lower surface meeting in a substantially sharpannular edge, adjacent surfaces of the upper and lower annular partsdefining between them an annular gas passage operatively connected to asource of pressurized gas and terminating in an annular gas orifice. Theedges and the gas orifice define a wire orifice through which passes awire coated with molten metal, which is therein wiped by the gas blownthrough the gas passage.

This gas wiping nozzle is efficient for wiping excess molten metal fromthe surface of a wire, but it can be easily damaged by molten metal.Indeed, during the coating process, the molten metal coated wire isgenerally drawn along a drawing axis centered in the wire orifice. Themolten metal coated wire can deviate from its drawing axis and contactsdirectly the annular gas passage, the molten metal thence filling in thegas passage, solidifying therein and therefore obstructing it. From thatpoint on, the molten metal coated wire passing through the nozzle is notproperly wiped and does no longer meet the quality requirements. The gaswiping nozzle has to be cleaned or replaced.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a gas wiping nozzlewhich avoids or alleviates the above-mentioned problems. According tothe present invention, this object is achieved by a gas wiping nozzleaccording to claim 1.

In accordance with the present invention, a gas wiping nozzle for a wirecoating apparatus comprises a passage for a wire being drawntherethrough along a central axis. This passage includes a converginginlet section through which the wire coated with molten metal entersinto the gas wiping nozzle, and a wiping section arranged downstream ofthe inlet section. The wiping section has a gas outlet means therein,which surrounds the passage for blowing wiping gas against the surfaceof the wire being drawn therethrough. In accordance with an importantaspect of the present invention, a protruding annular lip is arrangedbetween said converging inlet section and said wiping section. This lipdefines a narrower passage than said wiping section, so as to protectthe gas outlet means in the wiping section from direct contact with thecoated wire. The gas outlet means may include for example a continuousannular slit or several contiguous slits or orifices.

Such a lip arranged between the converging inlet section and the wipingsection of a nozzle provides an efficient protection for the gas outletmeans against direct contact with the molten metal coated wire. If awire deviates from the central axis, it will contact the lip and not thegas outlet means. Moreover, the molten metal will remain under the lipand flow down to the diverging section, since the lip protrudes into thepassage. The molten metal will consequently not fill the gas outletmeans, and the gas wiping nozzle will not have to be cleaned orreplaced.

Advantageously, the gas wiping nozzle includes contact detecting meansfor detecting a wire contacting said lip. The contact detecting meansmay include an electrically conductive ring arranged in an electricallyinsulated manner in the lip. It is easily understood that the metallicring together with the wire may serve as a switch for the contactdetecting means. A wire deviating from the central axis and contactingthe lip may trigger an alarm so that the operator will be warned and caneliminate the malfunction.

The gas wiping nozzle may also include position detecting meanssurrounding said passage, for detecting a wire deviating from thecentral axis of said passage. The position detecting means preferablyincludes temperature, inductive or optical sensors, or laser means.Thereby, the operator can be warned of an imminent malfunction andimmediately solve it.

Advantageously, a gas equalization chamber surrounds the passage in thegas wiping nozzle and communicates with the gas outlet means. Theequalization chamber acts for dynamic pressure homogenization at theentrance of the gas cutlet means, thus contributing to an axisymmetricwiping gas distribution in the passage.

The gas wiping nozzle may include pressure sensors for measuring thewiping gas pressure in the equalization chamber. It becomes therebypossible to correlate the coating thickness and the wiping gas pressure.

In a first embodiment, a turbine rotor is arranged in the equalizationchamber so as to be rotated by wiping gas injected into the equalizationchamber. The turbine rotor along with the equalization chamber furthercontribute to a more homogeneous wiping gas distribution. The morehomogeneous the air blast, the better the quality of the coating.

In a second embodiment, the turbine rotor defines part of the passagedownstream of the wiping section. The gas outlet means then includes anannular slit defined between upper and lower annular surfaces, the upperannular surface being a surface of the turbine rotor. At least onecleaning means is then preferably attached to the upper annular surfaceso as to clean the annular slit while the turbine rotor is rotated bythe wiping gas.

Rotation sensing means for measuring the number of revolutions per unitof time of the turbine rotor may also be used to correlate the coatingthickness and the number of revolutions per unit of time.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more apparent from the followingdescription of a not limiting embodiment with reference to the attacheddrawings, wherein

FIG. 1: is a longitudinal section of a first gas wiping nozzle;

FIG. 2: is a longitudinal section of the lip of the gas wiping nozzle ofFIG. 1;

FIG. 3: is a section AA of the gas wiping nozzle of FIG. 1;

FIG. 4: is a longitudinal section of a second gas wiping nozzle;

FIG. 5: is a longitudinal section of a third gas wiping nozzle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a longitudinal section of a gas wiping nozzle 10 that isused in a wire coating apparatus for wiping excess molten metal off thesurface of a wire coated with molten metal. A wire 12, represented byits axis, is drawn upwards from a molten metal bath 14 and passesthrough the nozzle 10 via a passage 16. It is drawn upwards byschematically represented drawing means 18, along a substantiallyvertical central axis 20, as shown by the arrow 21. The wire 12 entersthe nozzle 10 through a converging inlet section 22, wherein the sectionof the passage 16 decreases in the drawing direction. A wiping section24 situated downstream of the inlet section 22 comprises an annular gasoutlet slit 26, for blowing wiping gas against the surface of the moltenmetal coated wire 12 passing through the nozzle 10.

It shall be appreciated that a protruding annular lip 28 is arrangedbetween the inlet section 22 and the wiping section 24, preferably justbeneath the gas outlet slit 26. Such a lip 28 provides a localizedsection reduction just before the gas outlet slit 26, which is therebyprotected from direct contact with the molten metal coated wire 12.Indeed, a wire 12 deviating from the central axis 20 cannot come intocontact with the gas outlet slit 26 since the lip 28 will keep it spacedfrom the gas outlet slit 26.

FIG. 2 shows a longitudinal section of the lip 28. In order to detect awire 12 contacting the lip 28, a metallic ring 30 is arranged in anannular groove 32 in the lip 28. The metallic ring 30 is insulated fromthe body of the nozzle 10, and in particular from the lip 28, byinsulating material 34 inserted in the annular groove 32 between thering 30 and the nozzle 10. It can easily be understood that the metallicring 30 and the wire 12 serve as a switch that triggers an alarm in caseof contact between the wire 12 and the lip 28. An operator warned by thealarm can stop or intervene in the coating process to repair themalfunction.

Turning now to FIG. 3, four sensors 36 are arranged at the same leveldownstream the gas outlet slit 26, in the passage walls, and areregularly spaced about the circumference of the passage 16. These foursensors 36 are part of position detecting means, enabling the detectionof a wire 12 deviating from the central axis 20, before it contacts thelip 28.

The configuration shown in FIG. 3 is e.g. suitable for temperature orinductive sensors. The four sensors 36 deliver four signals which arepermanently compared to each other by the position detecting means. Whenthe wire 12 is in the center of the passage 16, i.e. aligned along thecentral axis 20, the four sensors 36 deliver the same signal. Hence, ifone of the signals differs from the others, the wire 12 has deviatedfrom the central axis 20.

It is possible to detect the position of the wire 12 by using opticalsensors, such as light beams and photoelectric cells.

A further possibility is the use of two perpendicular laser beamsimpinging on the wire 12. When a wire 12 deviates from the central axis20, the laser beam reflects on the opposite passage wall instead ofreflecting on the wire 12. The return time of the laser beam increases,thereby signaling the deviation of the wire 12.

FIG. 4 shows a longitudinal section of a second nozzle 38. As in FIG. 1,a wire 12 is drawn through the nozzle 38 along a central axis 20, via apassage 16, in the direction indicated by arrow 21. The wire 12 entersthe nozzle 38 through a converging inlet section 40, passes through awiping section 42, then through a tubular section 44, and exits thenozzle 38 through a diverging section 46. The wiping section 42comprises a gas outlet slit 26 for wiping excess molten metal off thesurface of the wire 12. A lip 28 equipped with a metallic ring 30,similar to the lip of FIG. 1, is located just before the gas outlet slit26. As explained above, the lip 28 protects the gas outlet slit 26 fromdirect contact with the wire 12. The arrow 48 indicates a gas inlet 49in an equalization chamber 50 surrounding the passage 16 andcommunicating with the gas outlet slit 26. A turbine rotor 52 isinstalled in the equalization chamber 50 and surrounds the passage 16 aswell. Wiping gas, e.g. nitrogen (N2), is supplied to the equalizationchamber 50 through the gas inlet 49 and impinges on the turbine rotor52, which is thereby rotated. The equalization chamber 50 and theturbine rotor 52 facilitate the homogenization of the pressure of thewiping gas, before being blown through the gas outlet slit 26.

Reference sign 53 generally indicates a pressure sensor installed in thebody of the nozzle 38, for measuring the wiping gas pressure in theequalization chamber 50. It is thereby possible to correlate thethickness of the molten metal coating and the wiping gas pressure in theequalization chamber 50.

It shall be noted that the nozzle 10 of FIG. 1 is also equipped with anequalization chamber 50 and pressure sensors 53.

Besides, a rotation sensing means is installed in the nozzle 38. Therotation sensing means comprises e.g. a magnet 54 embedded in theturbine rotor 52, and an inductive sensor 56 is installed in the body ofthe nozzle 38 so as to be on the trajectory of the magnet 54. Theinductive sensor 56 detects the presence of the magnet 54 once perrevolution. It is thereby possible to determine the number ofrevolutions per unit of time, and thereby to correlate the thickness ofthe molten metal coating with the number of revolutions per unit oftime. The flow rate, which is a function of the speed of the turbinerotor 52 and the pressure, may also be determined.

FIG. 5 shows a third embodiment of a gas wiping nozzle 58. As in FIG. 4,a wire 12 is drawn through the nozzle 58 along a central axis 20, via apassage 16, in the direction indicated by arrow 21. The structure of thepassage 16 is different: the wire 12 enters the nozzle 58 through aconverging inlet section 60, passes through a wiping section 62, thenthrough a diverging section 64. The wiping section 62 comprises a gasoutlet slit 26 for wiping excess molten metal of the surface of the wire12. A lip 28 equipped with a metallic ring 30, similar to the lip ofFIG. 1, is located just before the gas outlet slit 26. As explained, thelip 28 protects the gas outlet slit 26 from direct contact with the wire12.

In this third embodiment, the equalization chamber 50 is isolated fromthe passage 16 by a turbine rotor 66. In other words, a central channelthrough the turbine rotor 66 defines a part of the passage 16. It shouldbe noted that the gas outlet slit 26 is defined by upper and lowerannular surfaces 68 resp. 70. The upper annular surface 68 is part ofthe turbine rotor 66. Hence, when the turbine rotor 66 is rotated, dueto the wiping gas in the equalization chamber 50, the upper 68 annularsurface is rotated as well. Reference sign 72 generally identifies asmall brush. Three radial brushes 72 are preferably attached to theupper annular surface 68. When the turbine rotor 66 is rotated, thebrushes 72 sweep the lower annular surface 70 and the gas blast clearsthe gas wiping slit 26. This third nozzle 58 can be regarded as aself-cleaning nozzle 58. The rotation of the turbine rotor 66 may bestopped by electromagnetic or mechanical means (not shown), in order toallow cleaning only when desired.

It shall be noted that each of the gas wiping nozzles respectively 10,38 and 58 may be embodied as a split nozzle, consisting of two or morebody parts. Thus, the wire does not have to be threaded through thepassage of the nozzle, but rather the body parts are separated while thewire is positioned in the coating apparatus, and the body parts are thenbrought together in abutment about the wire.

1. A gas wiping nozzle for a wire coating apparatus comprising: an inletportion defining a converging inlet passage for a coated wire that isaxially drawn through said gas wiping nozzle; a wiping portion defininga wiping passage for said coated wire, downstream and in axial extensionof said inlet passage, said wiping portion including gas outlet meanssurrounding said wiping passage for blowing wiping gas onto said coatedwire; and a protruding annular lip arranged between said converginginlet passage and said wiping passage, wherein said annular lip definesa passage for said coated wire that is narrower than said wipingpassage, so that said gas outlet means in said wiping passage isprotected by said protruding annular lip against direct contact withsaid coated wire, which is axially drawn through said passages of saidgas wiping nozzle.
 2. The gas wiping nozzle as claimed in claim 1,further comprising contact detecting means for detecting a coated wirecontacting said annular lip.
 3. The gas wiping nozzle as claimed inclaim 2, wherein said contact detecting means includes an electricallyconductive ring arranged in an electrically insulated manner in saidannular lip.
 4. The gas wiping nozzle as claimed in claim 1, furthercomprising position detecting means for detecting a coated wire thatdeviates from the central axis of said passages in said wiping nozzle.5. The gas wiping nozzle as claimed in claim 4, wherein said positiondetecting means includes a thermal and/or inductive and/or opticalsensor.
 6. The gas wiping nozzle as claimed in claim 4, wherein saidposition detecting means includes at least one optical sensor and onelaser.
 7. The gas wiping nozzle as claimed in claim 1, furthercomprising an annular gas equalization chamber that is in communicationwith said gas outlet means.
 8. The gas wiping nozzle as claimed in claim7, further comprising at least one pressure sensor for measuring thewiping gas pressure in said equalization chamber.
 9. The gas wipingnozzle as claimed in claim 7, further comprising a turbine rotorarranged in said equalization chamber so as to be rotated by wiping gasinjected into said equalization chamber.
 10. The gas wiping nozzle asclaimed in claim 9, wherein said turbine rotor defines a passage forsaid coated wire, downstream and in axial extension of said wipingsection.
 11. The gas wiping nozzle as claimed in claim 10, wherein: saidgas outlet means includes an annular slit defined between upper andlower annular surfaces; said upper annular surface is a surface of saidturbine rotor; and at least one cleaning means is attached to said upperannular surface so as to clean said annular slit while said turbinerotor is rotated.
 12. The gas wiping nozzle as claimed in claim 9,further comprising rotation sensing means for measuring the number ofrevolutions per unit of time of said turbine rotor.